1. Field of the Invention
The present invention generally relates to the conversion of chemical energy to electrical energy and, more particularly, to the connection of a current collector for one of the electrodes of an electrochemical cell to its terminal pin by an intermediate coupler. Preferably, the current collector and terminal pin are of dissimilar conductive materials. The novel coupler of the present invention is particularly useful for joining a cathode current collector to a molybdenum terminal pin.
2. Prior Art
Recent rapid developments in small-sized electronic devices having various shape and size requirements necessitate comparably small-sized electrochemical cells of different designs that can be easily manufactured and used in these electronic devices. This is particularly the case in implantable biomedical devices such as hearing-assist devices, neurostimulators, pacemakers, drug pumps, cardiovascular defibrillators, and left ventricular assist devices. Preferably, the electrochemical cell is of a high energy density, such as afforded by lithium systems, whether they be of the primary or the secondary type. One commonly used cell configuration is a prismatic, case-negative cell design having an intermediate cathode flanked by opposed anode portions in contact with the casing and in electrical association with the cathode. The prismatic electrode assembly is typically of either a relatively elongated anode folding into a serpentine configuration with a plurality of cathode plates interleaved between the folds or of alternating anode and cathode plates.
A perspective view of a typical prismatic electrochemical cell 10 is shown in FIG. 1. The cell 10 includes a casing 12 having spaced-apart front and back side walls 14 and 16 joined by curved end walls 18 and 20 and a curved bottom wall 22. The casing has an open top closed by a lid 24. Lid 24 has an opening 26 used for filling the casing 12 with an electrolyte after the cell components have been assembled therein and lid 24 has been welded to casing 12. In its fully assembled condition shown in FIG. 1, a closure means 28 is hermetically sealed in opening 26 to close the cell. A cathode terminal lead 30 is electrically insulated from lid 24 and casing 12 by a glass-to-metal seal 32, as is well known to those skilled in the art.
U.S. Pat. No. 5,250,373 to Muffoletto et al. describes a prismatic cell having the cathode terminal lead 30 connected to a cathode current collector. This patent is assigned to the assignee of the present invention and incorporated herein by reference. As shown in FIGS. 2 and 3, the prior art cell has a casing 12 housing a multi-plate electrode assembly of a cathode electrode 34 in electrical association with an anode electrode. Cathode 34 comprises plates 36, 38 pressed together and bonded against a cathode current collector 40 while the anode comprises anode plates 42 and 44 in operative contact with the respective cathode plates 36, 38. The cathode current collector 40 is provided with a tab 46 extending outwardly therefrom. A distal end of tab 46 is welded to a planar end of a coupler 48. The other end of the coupler comprises a tube that receives the inner end of the terminal pin 30 welded therein. Pin 30 provides an external electrical connection to the cathode 34 while the casing 12 and lid 24 are in electrical contact with the anode and serve as the anode terminal for this case-negative electrochemical cell 10.
This prior art construction provides a reliable means of connecting the cathode terminal pin 30 to the current collector 40 in a multi-plate electrode assembly housed in a prismatic casing. However, in a jellyroll or flat-folded electrode assembly, a coupler having a shape extending along the longitudinal axis of the electrode assembly is more suitable. In that respect, the coupler of the present invention comprises a rod shape extending generally parallel to the longitudinal axis of the electrode assembly. This provides a greater surface area for connection to the one electrode for which it serves as the terminal as well as providing increased contact surface area for electron flow.